1. Field of the Invention
This invention relates broadly to semiconductor devices and signal processing circuits realized from such semiconductor devices. More particularly, this invention relates to semiconductor devices that provide high gain signal amplification for use as a building block in a variety of signal processing applications.
2. State of the Art
Operational amplifier circuits and other high gain amplifier circuits are typically realized by a multistage design. For example, several well known operational amplifier designs utilize a differential amplifier stage, a high gain stage, and an output buffer stage. The high gain stage may be a differential-input amplifier stage or a single-ended input amplifier stage. In these designs, the transistor count is typically on the order of thirty transistors. For high frequency applications, these designs may be realized with high-frequency transistors such as heterojunction bipolar transistors (HBTs) or pseudomorphic high electron mobility transistors (PHEMTs).
The large number of transistors and associated circuit elements that form an operational amplifier (or other high gain amplifier), encompass a relatively large area when such devices are realized as part of an integrated circuit and thus may be problematic when integrating the amplifier circuit as part of a monolithic integrated circuit. In addition, the large number of transistors and associated circuit elements consume power, which may be problematic in low-power applications, such as mobile battery-powered applications.
Thus, there remains a need in the art to provide an operational amplifier circuit/high gain amplifier circuit that has a small device count, thereby improving the integration capability of circuit as well as the power consumption of the circuit. In addition, there is a need for an operational amplifier circuit/high gain amplifier circuit that is suitable for monolithic integration with a broad range of electronic circuitry (such as FETs and bipolar type transistors, logic, etc), waveguides and other optoelectronic devices.